The present invention relates to an aqueous butadiene latex, particularly an aqueous butadiene latex that is compatible with an aqueous phenolic resin. The butadiene latex is especially useful in aqueous adhesive or primer compositions.
Various techniques are known to emulsion polymerize butadiene polymers to obtain an aqueous latex. For example, according to an English translation, DE-A-33 21 902 relates to an aqueous emulsion polymerization for making chloroprene rubber than involves polymerizing chloroprene, optionally with up to 50 weight percent of a copolymerizable monomer, in the presence of 0.5 to 5 weight percent of a rosin acid derivative and 0.1 to 10 weight percent of a polystyrene sulfonic acid derivative, based on the weight of the total monomers. Copolymers of 95 weight percent chloroprene/5 weight percent 2,3-dichlorobutadiene are exemplified. The addition of the polystyrene sulfonic acid was shown to reduce the adhesion of the chloroprene rubber to a metal mold.
U.S. Pat. No. 4,054,547 relates to a process for copolymerizing chloroprene and 0.5-10 weight percent (based on total monomers) of at least one styrene sulfonic acid or a water soluble derivative thereof in an aqueous medium to form latex particles. The addition of an ethylenically unsaturated co-monomer to the system is mentioned. 2,3-dichlorobutadiene is listed as a possible co-monomer.
U.S. Pat. No. 4,400,229 relates to an aqueous dispersion of a phenolic resole and a thermoplastic polymeric material or a rubber prepared by dissolving a solid thermoplastics material or a rubber into a liquid phenol; adding a nonionic or anionic surface active agent and/or protective colloid; adjusting the pH of the mixture to above 7; adding aqueous formaldehyde solution or a formaldehyde donor and heating the mixture to form a phenolic resole.
U.S. Pat. No. 4,500,692 relates to suspension polymerization of a vinyl aromatic monomer in the presence of an inorganic phosphate suspension system and sodium polystyrenesulfonate. The possibility of copolymerization of the vinyl aromatic monomer with a co-monomer is briefly mentioned. Butadiene is included in a list of possible co-monomers.
U.S. Pat. No. 5,051,461 relates to an emulsion of metal neutralized sulfonated copolymer of a conjugated diene and an ethoxylated alkylamine salt of styrene sulfonate, and a tackifier resin. U.S. Pat. No. 4,530,987 relates to a polymer of at least 80% by weight of a conjugated diene and a minor proportion of a metal or amine neutralized styrene sulfonate monomer.
U.S. Pat. No. 5,162,156 relates to a primer composition that includes (a) novolak phenolic resin and (b) a halogenated polyolefin. Dichlorobutadiene polymers are listed as possible halogenated polyolefins.
Commonly-assigned U.S. patent application Ser. No. 08/889,294, filed Jul. 8, 1997, relates to an aqueous adhesive composition that includes a halobutadiene homopolymer latex, an aqueous soluble or dispersible phenolic resin and a maleimide-based compound. 2,3-dichloro-1,3-butadiene is the preferred halobutadiene monomer.
U.S. Pat. Nos. 5,200,459; 5,300,555; and 5,496,884 disclose emulsion polymerization of dichlorobutadiene monomers in the presence of polyvinyl alcohol and a co-solvent such as an organic alcohol or a glycol. Polyvinyl alcohol-stabilized dichlorobutadiene latex has been successfully commercialized, but it has a few drawbacks.
In particular, the use of a volatile organic co-solvent requires its removal from the emulsion latex. If not all the co-solvent is removed, the resulting latex may have an unacceptably high amount of volatile organic compounds (VOC). In addition, a high concentration of surfactants is used in the emulsion polymerization. High concentration of surfactants in adhesive compositions may cause the well-known “surfactant penalty” problem in the performance of the adhesive. The latex also suffers from compatibility problems when mixed with a water soluble phenolic resin or an aqueous dispersion or emulsion of a phenolic resin. A butadiene latex that alleviates these problems would be very desirable.